In general, plastic films have a strong tendency to be electrified, which places various restrictions on their uses. In silver halide photographic light-sensitive materials, for example, supports such as polyester films are generally used; therefore, these light-sensitive materials are liable to be electrified especially in a low humidity climate such as winter. In the recent tendency of photographic industry to use high speed coating of high-speed photographic emulsions and to expose high-speed light-sensitive materials through automatic printers, appropriate antistatic measures cannot be dispensed with.
When a light-sensitive material is electrified, it comes to cause static marks by discharging the accumulated electricity or to attract foreign matters such as dust which causes pinholes, and thereby the quality is deteriorated to a marked degree. If such troubles once occur, the correction thereof impairs the work efficiency greatly.
As antistatic measures for plastic films, there have been employed a method to incorporate an anionic compound such as organic sulfonate or organic phosphate, a method to vapor-deposit a metal compound, and a method to coat an anionic compound, cationic compound or so-called conductive compound. The method of incorporating an anionic compound is inexpensive, but cannot provide an enough antistatic effect. Further, it has disadvantages attributable to low molecular weights of the compounds to be incorporated; namely, it is liable to cause blooming, lowering in adhesion to a coating layer, poor water resistance and migration of said compound. The vapor deposition of metal compounds can provide an good antistatic property and has come to be used as a method to prepare a transparent conductive film, but it needs a high manufacturing cost. A method to coat a conductive carbon black or a conductive metal particles can impart a good antistatic property at a relatively low cost, but film transparency is lowered.
Under these circumstances, there is generally used the method to coat an anionic compound or cationic compound on a plastic film.
As antistatic agents for the light-sensitive material, there are recently used fluorine-containing surfactants, cationic surfactants, amphoteric surfactants, polyethylene-oxide-group-containing surfactants or polymers, and polymers containing a sulfonic group or phosphoric group in the molecule.
Particularly, control of electrification rank with a fluorine-containing surfactant and conductivity enhancement with a conductive polymer have come to be widely used. For example, Japanese Pat. O.P.I. Pub. Nos. 91165/1974 and 121523/1974 disclose the use of ionic polymers having a dissociated group in the principal chain.
However, these conventional methods cannot avoid a sharp drop in antistatic property in the course of development. This is attributed to the reduction of antistatic property in the processes of developing with alkaline compounds, fixing in an acid medium, and washing. Therefore, troubles such as generation of pinholes due to adsorption of dust are liable to occur, when printing is made using a film processed beforehand like a light-sensitive material for printing.
As a measure to prevent such a problem, an antistatic layer consisting of a carboxyl-group-containing hydrophobic polymer and a polyfunctional aziridine is proposed in Japanese Pat. O.P.I. Pub. Nos. 84658/1980 and 174542/1986. In this method, the antistatic property can be retained after development. But this method has a disadvantage that the antistatic layer is poor in adhesion to a hydrophilic colloid layer such as an antistatic layer coated on a plastic film including polyester film.
On the other hand, Japanese Pat. Exam. Pub. No. 3437/1955 and Japanese Pat. O.P.I. Pub. Nos. 57722/1984 and 250041/1985 disclose techniques to enhance a barrier property against water and gases and to improve dimensional stability and water resistance by coating a vinylidene chloride copolymer layer on a polyester film.
However, these techniques have a problem in the balance between the barrier property and the adhesive property, and therefore enhancement of the barrier property tends to weaken the adhesive property.